Web traffic reduced to its simplest case happens synchronously between two parties: Me, the client, and the server providing the resource I want to access. Encr

Web traffic reduced to its simplest case happens synchronously between two parties: Me, the client, and the server providing the resource I want to access. Encrypting the communication between those two points breaks various people in-between who want to listen in with varying degrees of legitimacy (others can't listen in on my traffic, but on the other hand I can't e.g. listen in on the traffic of IoT-devices in my home network any more, either), but it doesn't break anything a regular end user might immediately care about. Mail traffic is different: So that the sender and the receiver don't have to be online a the same time, we also need another intermediate party, i.e. the mail server. (In practice both sender and receiver utilise a mail server as an intermediate party, but here I'm mainly interested with "my" mail server on the receiving side.) If the mail server's role was purely restricted to being a dumb store-and-forward store to hold any mails that arrive when I'm not online then, that'd be the end of the story, but in practice the mail server also fulfils a few additional functions that only work if the server actually has access to the message contents: - Easy access from various sorts of mail clients ranging from full computers to phones to (especially for regular users these days) webmail, without having to worry about anything complicated like key management or whatnot - Server-side spam filtering - Server-side search, especially for mobile clients and webmail